Governmental efforts to encourage recycling of paper and packaging materials began over two decades ago. Since then, large volumes of recycled paper have become available. Several steps involved in the process of paper-making are also used to convert recycled paper to reusable pulp (such as forming an aqueous slurry of paper or wood fibers and spreading these slurries into a thin layer to permit excess moisture to drip out). Therefore, one could have reasonably expected that numerous novel products would be developed based on or incorporating recycled paper.
In fact, paper pulp is mixed with a wide variety of chemical materials in paper-making processes. The chemical materials combined with paper pulp in paper making include surfactants, starch, and polymeric fibers. For example, an anionic surfactant used in the aqueous solvent of U.S. Pat. No. 4,347,100 (at a level of 0.4-0.7% by weight of the weight of cellulose used) is said to remove lignin from cellulose fibers, dispersing the fibers more easily and thoroughly in the pulp. Nonionic surfactants of U.S. Pat. No. 4,766,030 are said to debond wood pulp and improve pulp wettability. The surfactant blend of U.S. Pat. No. 5,139,616 is said to facilitate removal of adhesives from recycled paper pulp to improve the resultant paper. Paper pulp has also been combined with starch (U.S. Pat. No. 4,347,100) and synthetic materials. The pulps of U.S. Pat. No. 5,169,447, derived from combinations of wood and recycled paper, are mixed with at least 0.0007% by dry weight of polymer to improve pulp "freeness" and the quality of the resulting paper.
Surfactants are also used to treat compositions based on synthetic fibers. In U.S. Pat. No. 4,766,939, surfactants are used to lubricate synthetic fibers such as glass. The nonionic alkylene oxide adducts of U.S. Pat. No. 5,232,628 are said to be suitable for treating polymeric fibrous materials.
Although large volumes of cellulose pulp are processed in paper-making in large volumes, gas and air are not to be incorporated into pulp. Indeed, such aeration is to be avoided, according to U.S. Pat. Nos. 4,766,030 and5,232,628. By contrast, air is introduced into the fibrous slurry of U.S. Pat. No. 4,576,716; it is said to cause fibers suspended in the slurry to become entangled with one another, not to form a stable aerated slurry. These entangled fibers are said to coalesce into fiber lumps, which are then more easily formed into filtration materials when dry.
Because paper pulp is mixed with such a wide variety of chemical materials, one could have reasonably expected that a wide range of conventional products could be modified by incorporation of recycled paper. Commercial products which incorporate recycled paper however tend to have shortcomings which decrease their efficiency or performance. For example, an agricultural ground cover, used to protect newly sown seeds or to prevent weed growth near cultivated crops, comprises an aqueous slurry of paper fibers. These slurries, having a density of 0.3 to 0.7 g/cc, were initially introduced to avoid the need to retrieve conventional cloth ground covers (e.g., burlap) from fields. The seemingly more convenient paper slurry however introduced a significant problem into the use of ground covers: in preparing the paper slurry cover, a precise ratio between the water to paper fiber contents must be met. If the composition is made with even a slight excess of paper, the resulting material is easily displaced by a slight breeze. If however, the composition is made with even a slight excess of water, the resulting ground cover can be too heavy and dense for rain to penetrate or for seedlings to grow through; furthermore, this dense composition may remain as an impediment to cultivation after one growing season.
Another commercial product which incorporates recycled newspaper is cellulose-based heating insulation. This material is comprised of approximately 100 parts by weight of ground newspaper, 35-45 parts by weight of fire retardant and optional components such as dye. The composition is mixed and applied by a blower into wall spaces and has a density of from 3.5 to 4.5 pounds per cubic foot. (0.05-0.06 g/cc). This density and the amount of fire retardant agent needed to impart fire retardancy to the material are undesirably high.